Time-delay circuit for automatic shutdown of furnace systems

Abstract

Time-delay circuit for automatic shutdown of furnace systems has an induced draft blower motor and a first circuit for providing energy to the blower motor from an energy source. A second circuit for energizing the primary control system of the furnace, includes a thermostat and an electronic switching means. When the thermostat is "closed", the second circuit is completed to energize the electronic switching element which starts the blower. An airflow switch is provided to sense the start of the blower and to thereby energize a primary control which provides gas to a burner of the furnace. A timer set to a predetermined time interval has an output and two input terminal connections, one connected to the output of the thermostat and another to the output of the primary control system. When the thermostat is "closed" and the burner is operating, the timer is disabled. However, when the thermostat is "closed" and the burner is not operating such as occurs during "lockout" conditions, upon elapse of the predetermined time interval, the timer output interrupts power to the electronic switching means, thereby shutting "off" power to the primary control and to the blower motor.

Having thus described my invention, what is claimed is: 
     
       1. In a time-delay circuit for automatic shutdown of furnace systems having a power source connected to an induced draft blower motor, a primary burner control adapted to energize a fuel valve of the furnace, a relay controller adapted to control the operation of the induced draft blower motor and the primary burner control, a thermostat connected to supply energy selectively to the primary burner control and to a first electronic switching means connected, when conductive, to energize said relay controller, a second electronic switching means is connected, when conductive to turn "off" the first electronic switching means, the improvement comprising a timer including connections for at least a first and a second input and one output, the first input of said timer being connected to receive energy from the thermostat, the second input being connected in circuit with the primary burner control and the fuel valve so that when the primary control energizes said fuel valve, the timer is also energized, the output of said timer being connected to said second electronic switching means so that when said timer generates an output signal, the second electronic switching means will be turned "on", said second electronic switching means being adapted to divert energy from and turn "off" said first electronic switching means to de-energize the relay controller and thus cut "off" both the primary burner control and the induced draft blower. 
     
     
       2. In a time-delay circuit for automatic shutdown of furnace systems, as set forth in claim 1, wherein said timing means comprises a computer chip. 
     
     
       3. In a time-delay circuit for automatic shutdown of furnace systems, as set forth in claim 1, wherein said first input includes an alternating current rectifying circuit comprising a diode and a capacitor. 
     
     
       4. In a time-delay circuit for automatic shutdown of furnace systems, as set forth in claim 1, wherein said second input also includes an alternating current rectifying circuit comprising a diode and a capacitor. 
     
     
       5. In a time-delay circuit for automatic shutdown of furnace systems, as set forth in claim 1, wherein said timer includes a reset pin which is connected to said second input lead.